1. Field of the Invention
The present invention relates to an improvement in the rechargeable batteries in which chemical reaction with lithium is utilized (these rechargeable batteries will be hereinafter collectively referred to as rechargeable lithium battery) and also in the rechargeable zinc series batteries. More particularly, the present invention relates to an improvement in the rechargeable lithium batteries and rechargeable zinc series batteries so that they are always highly safe and stably exhibit an excellent current collecting performance while preventing occurrence or growth of a dendrite (or a branched tree-like protrusion) of lithium or zinc upon repetition of charging and discharging, and they are long enough in cycle life (in other words, they have a prolonged charging and discharging cycle life). The present invention includes a process for the production of an improved lithium battery and an improved zinc series battery.
2. Related Background Art
In recent years, heating of the earth because of the so-called greenhouse effect due to an increase of atmospheric CO.sub.2 has been predicted.
In the case of the steam-power generation, the amount of a fossil fuel represented by coal or petroleum to be consumed for power generation in order to comply with a societal demand for increased power supply has been continuously increased and along with this, the amount of exhaust fumes from the steam-power generation plants has been continuously increased accordingly to raise the content of gases to cause a greenhouse effect such as carbon dioxide gas in the air. This results in providing an earth-warming phenomenon. In order to prevent said earth-warming phenomenon from further developing, there is a trend of prohibiting the establishment of a new steam-power generation plant in some countries.
Under this circumstance, a proposal has been made to conduct so-called load leveling in order to effectively utilize the power generator, wherein rechargeable batteries are installed at general houses and a surplus power unused in the night. That is, a so-called dump power, is stored in said rechargeable batteries and the power thus stored is supplied in the daytime when the power demand is increased, whereby the power generator is leveled in terms of the load therefor.
By the way, there is an increased societal demand for developing a lightweight rechargeable battery with a high energy density for an electric vehicle which does not exhaust any air polluting substance such as CO.sub.x, NO.sub.x, SO.sub.x, hydrocarbon, and the like. In addition to this demand there is an increased societal demand for developing a miniature, lightweight, high performance rechargeable battery usable as a power source for potable instruments such as small personal computers, word processors, video cameras, and pocket telephones.
As such rechargeable battery, there has been proposed a rocking chair type lithium ion cell in which a lithium intercalation compound is used as a cathode active material and carbon is used as an anode active material. However, as of the present time, there has not been realized a practical usable lithium ion battery having a sufficiently high energy density, which is considered could be attained by using a metallic lithium as the anode active material.
The public attention has now focused on the rechargeable lithium battery in which metallic lithium is used as an anode, but as of the present time, there has not been a practical usable, high capacity rechargeable lithium battery with an improved energy density attained. Particularly, as for the known rechargeable lithium battery, there is a problem in that lithium is often deposited in a dendritic state (that is, in the form of a dendrite) on the negative electrode (or the anode) during the charging operation, wherein such deposition of lithium in a dendritic state results in causing internal shorts or self-discharge. In the worst case, such dendritic deposition breaks through a separator, which is usually disposed between the anode and the cathode, to reach the cathode, resulting in causing internal-shorts between the anode and the cathode.
As one of the reasons why such practically usable, high capacity rechargeable lithium battery as above described has not yet realized, there is a fact that a manner capable of preventing the occurrence of the above dendritic deposition has not developed.
Now, as above described, when the above lithium dendrite is once formed, the dendrite is liable to gradually grow upon the charging operation, resulting in causing internal-shorts between the anode and the cathode. When the anode is internally shorted with the cathode as above described, the energy possessed by the battery is shortly consumed at the internally shorted portion to entail problems such that the battery is heated or the solvent of the electrolyte is decomposed by virtue of heat to generate gas, resulting in raising the inner pressure of the battery. These problems result in damaging the rechargeable battery or/and shortening the lifetime of the battery.
There has been proposed a manner of using a lithium alloy such as lithium-aluminum alloy as the anode for a rechargeable lithium battery in order to suppress the reactivity of the lithium so that a lithium dendrite is hardly generated. This manner is effective in preventing the generation of the lithium dendrite but is not effective in attaining a rechargeable lithium battery having a high energy density and which is long enough in cycle life.
Particularly, Japanese Unexamined Patent Publication No. 13264/1988 (hereinafter referred to as document 1), No. 47381/1993 (hereinafter referred to as document 2) or No. 190171/1993 (hereinafter referred to as document 3) discloses a non-aqueous series rechargeable battery in which the anode is constituted by a lithium alloy. Particularly, of these documents, the document 3 discloses a non-aqueous series battery aiming at an improvement in the cycle life and also in the cycle characteristics after having been stored, in which the anode is constituted by a material comprising an aluminum-manganese alloy added with a metal which is more electrochemically noble than aluminum such as vanadium, chromium, or titanium, and lithium as the anode active material, wherein the active site of said alloy with said lithium is increased to prevent localization of the reaction.
Further, Japanese Unexamined Patent Publication No. 114057/1988 (hereinafter referred to as document 4) discloses a non-aqueous series rechargeable battery aiming at an improvement in the charging and discharging characteristics, in which the anode is constituted by a basic constituent comprising a sintered body of a mixture composed of fibrous aluminum and fibrous metal incapable of being alloyed with lithium and a negative material comprising a lithium-aluminum alloy.
In addition, Japanese Unexamined Patent Publication No. 234585/1993 (hereinafter referred to as document 5) discloses a non-aqueous series rechargeable battery aiming at minimizing the generation of a dendrite so that the charging efficiency is improved and the battery cycle life is prolonged, in which the anode is constituted by a member made of lithium metal, having powdery metal (which hardly forms an intermetallic compound with said lithium metal) uniformly deposited on the surface thereof.
However, any of the rechargeable batteries disclosed in the above documents 1 to 5 is still problematic in that as the charging and discharging are alternately repeated over a long period of time, the anode is repeatedly expanded and shrunk to often suffer from a removal of the constituents or from a crack, wherein the generation or growth of a dendrite cannot be sufficiently prevented and the rechargeable battery eventually becomes poor in current collecting performance.
Other than the above-mentioned documents, Journal of Applied Electrochemistry, 22, 620-627 (1992) (hereinafter referred to as document 6) discloses a rechargeable lithium battery in which the anode is constituted by an aluminum foil having a surface applied with etching treatment. However, the rechargeable lithium battery disclosed in the document 6 is problematic in that when the charging and discharging cycle is repeated as many as that practically conducted for the ordinary rechargeable battery, problems are liable to entail in that as the charging and discharging are alternately repeated, the aluminum foil is repeatedly expanded and shrunk to suffer from a crack, resulting in causing a reduction in the current collecting performance, wherein the growth of a dendrite is liable to occur.
Hence, any of the rechargeable batteries disclosed in the documents 1 to 6 is still accompanied by some problems required to be solved.
The above situation in the conventional rechargeable lithium batteries is similar in the conventional rechargeable nickel-zinc batteries, rechargeable zinc-oxygen (or zinc-air) batteries and rechargeable bromine-zinc batteries. That is, in any of these zinc series batteries, the foregoing problems relating to the occurrence of a dendrite in the rechargeable lithium batteries are liable to often occur and therefore, it is difficult to attain a high energy density and a prolonged cycle life.
Accordingly, there is an increased demand for provision of an improved, highly reliable rechargeable battery which is high in energy density (or charge energy density) and long enough in charging and discharging cycle life.